I'm not sure what a travel story is supposed to mean.
A story has a problem for the MCs to solve, an answer to find, something to discover. Most of my stories involve travel and discovering new things. If Frodo, in Lord of the Rings, did not have to travel to all kinds of new and interesting places, there wouldn't be a book!
Just tourists going on a trip is generally not that interesting. They need a mission, some underlying reason to go to these cities and look around. They are trying to find something. Solve a mystery. Find out what happened to somebody they know. Find out what happened 25 years ago. Or maybe they are trying to solve a puzzle that is a hundred years old: They found a new clue, and there may be a treasure at the end.
Also, although setting can be excellent, in general for a story what we are interested in is the MCs. What they think, how they feel, their relationships with each other (or others) and how those relationships are changing, or how their lives are changing. If they are new adults, this may be the last real trip they can take together, they have just graduated college and will soon disperse: The military, two jobs, and graduate school.
If they are looking for something, somebody can oppose them; you have a villain.
But you don't have to have a villain, the circumstances they are in can be the villain. They get lost. They get robbed. One of them is in love with another, and this trip is the last chance to do anything about it.
The setting is always the background. It can be most of the story, like Lord of the Rings, and it can seem to dominate the writing, it can be very interesting, but it is the background. You need a story, a struggle, a mission, to drive the characters through the setting, so you can show it to the reader.